The Parthian horse, like the Persian, was of two kinds, standing in strong contrast the one to the other. The bulk of their cavalry was of the lightest and most agile description. Fleet and active coursers, with scarcely any caparison but a headstall and a single rein, were mounted by riders clad only in a tunic and trousers, and armed with nothing but a strong bow and a quiver full of arrows. A training begun in early boyhood made the rider almost one with his steed; and he could use his weapons with equal ease and effect whether his horse was stationary or at full gallop, and whether he was advancing towards or hurriedly retreating from his enemy. His supply of missiles was almost inexhaustible, for when he found his quiver empty, he had only to retire a short distance and replenish his stock from magazines, borne on the backs of camels, in the rear. It was his ordinary plan to keep constantly in motion when in the presence of an enemy, to gallop backwards and forwards, or round and round his square or column, never charging it, but at a moderate interval plying it with his keen and barbed shafts which were driven by a practised hand from a bow of unusual strength. Clouds of this light cavalry enveloped the advancing or the retreating foe, and inflicted grievous damage without, for the most part, suffering anything in return. But this was not the whole. In addition to these light troops, a Parthian army comprised always a body of heavy cavalry, armed on an entirely different system. The strong horses selected for this service were clad almost wholly in mail. Their head, neck, chest, even their sides and flanks, were protected by scale-armor of brass or iron, sewn, probably, upon leather. Their riders had cuirasses and cuisses of the same materials, and helmets of burnished iron. For an offensive weapon they carried a long and strong spear or pike. They formed a serried line in battle, bearing down with great weight on the enemy whom they charged, and standing firm as an iron wall against the charges that were made upon them. A cavalry answering to this in some respects had been employed by the later Persian monarchs, and was in use also among the Armenians at this period; but the Parthian pike was apparently more formidable than the corresponding weapons of those nations, and the light spear carried at this time by the cavalry of a Roman army was no match for it.